This invention relates to a 3-wheeled, generally in-line, articulated landing gear with the lever trailing the lever hinge axis and, more particularly, an aircraft landing gear in which the entire rolling assembly, including the shock strut, twists 90.degree. upon retraction.
Design of an aircraft main landing gear is a compromise between many conflicting requirements, thus limiting near optimum selection to a small number of the total elements required. Fundamentally, an inventor must select between a telescopic leg and an articulated levered unit and also determine whether the gear is in the stowed position is to be contained within the loft lines of the normal fuselage or a pod or blister outside the normal loft lines. The conflicting requirements include wheel flotation, turning complexity, gear retraction, landing behavior, backing and braking, stability, free fall, pod drag, weight, maintenance, cost, reliability, and how the gear integrates with the aircraft structure. Aircraft having a requirement to land and take off from airstrips having a low bulk modulus of elasticity, which produce high drag loads, suggest a levered suspension unit landing gear with a trailing beam, as it provides greater resiliency. Gear stowage inside or outside the normal fuselage loft line is generally determined by the vertical clearance available for stowage which is often dictated by the floor location. Judicious trade-off of many elements is required to produce a combination which functions as a satisfactory main gear.
Generally, it is axiomatic that the fewer tires per gear pattern, the more efficient each tire. Of course, this must be balanced against maximum wheel size as determined by other criteria.
There are no known applications in cargo or commercial aircraft where three generally aligned wheels are used on a single strut. However, there is a military airplane, the SR71 and its associated models which use three wheels in line. In the SR71, the strut structure is a fork type which straddles the center wheel with another wheel on either side which is supported by a cantilevered axle. The center wheel is inaccessible and clearly distinguishable over the present invention.
Prior art landing gears have rotated and folded upon retraction, used laterally offset posts, and have mechanically synchronized the various kinematics. It is the unique combination of these features in a single landing gear along with the new axle beam arrangement, which makes this landing gear distinguishable over the prior art.
It is an object of this invention to provide a landing gear with a highly efficient wheel arrangement to provide superior wheel flotation for application with low bulk modulus of elasticity landing strips yet providing good turning ability without main gear steering while providing excellent landing stability. It is a further object of this invention to provide a retracting mechanism which provides for stowage in a minimum sized pod external to the normal fuselage line which results in minimum aerodynamic drag and yet provide a gear capable of free falling in the event of loss of the main gear actuator.
It is yet another object of this invention to provide a landing gear where all the wheels are readily removable and their brakes are readily accessable.